Enzymatic and metabolic responses to affluent diet of two diabetes-prone species of spiny mice: Acomys cahirinus and Acomys russatus

The adaptive responses to sucrose and fat diets were investigated in two species of spiny mice, Acomys russatus and Acomys cahirinus, in relation to their propensity to develop diabetic-like symptoms. A russatus gained weight pronouncedly, both on regular and fat-rich seed diet, did not exhibit hyperglycemia or hyperlipidemia but had highly increased hepatic triglyceride content in association with high levels of circulating free fatty acids and incidence of ketonuria in 10 of 41 animals. On the other hand, A. cahirinus exhibited a moderate weight gain on the fat diet which was accompanied by hyperglycemia but no hyperlipidemia or ketonuria. Neither weight gain nor ketonuria were evident in A. russatus and A. cahirinus on the sucrose-rich diet, but there was hyperlipidemia in the latter species. A. cahirinus, in particular, showed many-fold induction of liver enzymes, of regulatory importance in the pathways of glycolysis and lipogenesis, which could be linked to the hyperlipidemia in this species. On the fat diet there was a smaller increase in activity in enzymes related to gluconeogenesis in A. russatus compared with A. cahirinus, as well as a smaller suppression of glycolytic and lipogenic enzymes. Adipose tissue lipoprotein lipase activity rose in response to the fat-rich diet, more markedly in A. russatus than A. cahirinus in correlation to the more marked weight gain and hyperinsulinemia in this species. The affluent diets, especially sucrose, elicited an increase in circulating triiodothyronine levels which was more pronounced in A. cahirinus than in A. russatus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Discrimination between full-sibling spiny mice (Acomys cahirinus) by olfactory signatures

Discrimination between individual full siblings was tested in spiny mice (Acomys cahirinus). At weaning, intact litters were separated into two pairs so that animals only had social contact with one of their full siblings. Following 10 days of being housed in pairs, the four weanlings from a given litter were reunited in an observation terrarium. Pairings by familiar siblings were more frequent than unfamiliar-sibling pairings, indicating that interactions among close kin are mediated by the recognition of individual signatures rather than general phenotypic traits shared by all members of a kin class. Animals rendered anosmic by intranasal injections of zinc sulphate displayed no evidence of discriminating between familiar and unfamiliar siblings. Olfactory cues therefore appear to function as the signatures by which individual siblings are recognized. Since all animals were fed identical diets and otherwise maintained in similar environments, the differences in olfactory signatures between full siblings are most likely a function of genetic variability within this class of kin.     

Reproductive and metabolic responses of desert adapted common spiny male mice (Acomys cahirinus) to vasopressin treatment

Sufficient amounts of water and food are important cues for reproduction in an unpredictable environment. We previously demonstrated that increased osmolarity levels, or exogenous vasopressin (VP) treatment halt reproduction of desert adapted golden spiny mice Acomys russatus. In this research we studied gonad regulation by VP and food restriction (FR) in desert adapted common spiny mouse (A. cahirinus) males, kept under two different photoperiod regimes-short (SD-8L:16D) and long (LD-16L:8D) days. Mice were treated with VP, FR, and VP+FR for three weeks. Response was assessed from changes in relative testis mass, serum testosterone levels and mRNA receptor gene expression of VP, aldosterone and leptin in treated groups, compared with their controls. SD-acclimation increased testosterone levels, VP treatment decreased expression of aldosterone mRNA receptor in the testes of SD-acclimated males. FR under SD-conditions resulted in testosterone decrease and elevation of VP- receptor gene expression in testes. Aldosterone receptor mRNA expression was also detected in WAT. These results support the idea that water and food availability in the habitat may be used as signals for activating the reproductive system through direct effects of VP, aldosterone and leptin on the testes or through WAT by indirect effects.     

Comparative non-shivering thermogenesis in adjacent populations of the common spiny mouse (Acomys cahirinus) from opposite slopes: the effects of increasing salinity

We compared non-shivering thermogenesis between two adjacent populations of the common spiny mouse Acomys cahirinus from different habitats, in relation to increasing salinity. Individuals were captured from the north- and south-facing slopes of the same valley, that represent "Mediterranean" and "desert" habitats, respectively. We hypothesized that the two populations of mice would differ in their thermoregulatory capacities, reflecting their need to cope with the environmental stress in each habitat. We measured resting metabolic rate by recording oxygen consumption, body temperature and response to an injection of exogenous noradrenaline. Mice were maintained on diets with increasing levels of salt intake to examine their abilities to cope with increasing osmotic stress. Mice from north-facing slopes generally had a higher resting metabolic rate and a higher increase in oxygen consumption in response to noradrenaline than mice from south-facing slopes. Increasing salinity decreased resting metabolic rate values, body temperature, and oxygen consumption in response to noradrenaline in both populations, and diminished slope-dependant differences. We suggest that these differences could be a result of an ongoing adaptive process to different climatic conditions, typical of the Mediterranean region, that are a demonstrable example of evolution in action.     

Characterization of social behavior in the spiny mouse,Acomys cahirinus

While there are many species that are commonly used for the study of mammalian social behavior, there remains a need for lab-suitable organisms that are appropriate for examining sociality specifically in non-reproductive contexts (i.e., social behavior not in the context of mating or parenting). The spiny mouse, Acomys cahirinus, is a cooperatively breeding rodent that lives in large groups and is a species that holds great potential for studying a wide range of social behaviors in reproductive and non-reproductive contexts. Here, we characterize the basic social behaviors in male and female A. cahirinus to obtain a foundation for future study. We tested adult A. cahirinus in social approach, social preference, social interaction, social recognition, and group size preference paradigms. Regardless of sex, novelty, or familiarity, we found that both males and females rapidly approach conspecifics demonstrating high social boldness. Additionally, both sexes are significantly more prosocial than aggressive when freely interacting with conspecifics. However, we observed effects of sex on social preferences, such that males exhibit a preference to affiliate with same-sex conspecifics, whereas females exhibit a preference for affiliating with opposite-sex conspecifics. We discuss how this preference may relate to the cooperative breeding system of spiny mice. Lastly, both sexes show a robust preference for affiliating with large over small groups, indicating they may be an ideal species for the study of mammalian gregariousness. These data lay a basic foundation for future studies that seek to assess complex group dynamics and the mechanisms underlying reproductive and non-reproductive social behaviors in a highly social mammal.     

Ultrastructure of Kolmer's crystalloid in the pinealocytes of the common spiny mouse (Acomys cahirinus dimidiatus)

Light-and electron-microscopical observations revealed a rod-like inclusion body in the pinealocytes of the common spiny mouse (Acomys cahirinus dimidiatus). Ultrastructurally, the body is composed of a varying number of tubes whose wall consists of thin filaments aligned in helical arrangement. The inner and outer surface of the wall is covered with ribosome-like granules. Based on a morphological analysis it is concluded that the body described in the present investigation is identical with Kolmer's crystalloid of horizontal cells in the human and primate retina.This work represents a portion of a doctoral thesis (Dr. med.) submitted to the University of Bonn and was presented at the 87th meeting of the anatomische Gesellschaft in Mainz, Germany, March 1992     

Intestinal helminths of spiny mice (Acomys cahirinus dimidiatus) from St Katherine's Protectorate in the Sinai, Egypt

Spiny mice, Acomys cahirinus dimidiatus, inhabiting the wadis close to St Katherine in the mountains of the Sinai peninsula, were trapped and their helminth parasites were studied. Sixty one mice provided faeces for analysis and 27 were killed and autopsied. Six species of helminths were recorded (the spirurid nematodes, Protospirura muricola (74.1%) and Mastophorus muris (11.1%), the oxyuroid nematodes, Dentostomella kuntzi (59.3%), Aspiculuris africana (3.7%), and Syphacia minuta (3.7%) and the hymenolepidid cestode Rodentolepis negevi (18.5%)). The spirurids were the dominant species present, accounting for up to 0.87% of total host body weight. Analysis of worm weights and lengths suggested that transmission had been taking place in the months preceding our study. No sex difference in the prevalence or abundance of spirurids was detected. Significant differences were identified in the abundance of total nematode burdens and the mean helminth species richness between the three wadis which provided multiple captures of mice. There was also a marked effect of host age on both parameters. A highly significant positive correlation between spirurid egg counts and total worm biomass indicated that non-invasive techniques based on egg counts could be used to quantify worm burdens and when this technique was applied to a larger sample size (n = 61), a significant difference between sites but no host sex or age effects were detected for spirurid faecal egg counts. The data suggest that there are differences between helminth component communities infecting spiny mice in different neighbouring wadis, a hypothesis which will be explored further through our continuing studies in the Sinai.     

Opioid modulation of ingestive behaviors in the spiny mouse (Acomys cahirinus)

Feeding and drinking behavior were studied in deprived or sated spiny mice (Acomys cahirinus) at various time intervals following peripheral administration of naloxone hydrochloride and butorphanol tartrate. Naloxone attenuated both food and water intake, but not latency to respond, indicating existence of functional opioid-sensitive feeding and drinking systems in this species. Butorphanol tartrate, a mixed opioid agonist/antagonist produced a dose-related enhancement or suppression of feeding, the former naloxone reversible, but had no measureable effect on drinking.     

The structure of the spiny mouse (Acomys cahirinus) ovary during development

The study presents the structure of the ovaries of the spiny mouse (Acomys cahirinus) during the first months of life. The ovaries in neonate females exhibit a large number of primordial and primary follicles, sometimes clustered in nests. The growing follicles were also observed within the ovary at that period. The first, early antral follicles appeared in the ovary during the second week of life. In the group of 60-day old females, the structure of the ovaries was characterized by a significant increase in the connective tissue elements. Moreover, ovarian follicles at various stages of development were observed, except for the antral ones with cumulus oophorus. The first mature follicles were identified in 3-month old females. In the ovarian follicles, apoptosis occurs at all stages of follicle development, especially in the early antral follicles. In the atretic follicles, apoptotic cells were identified in the layer of granulosa cells.     

Diet selection and energy and water budgets of the common spiny mouse Acomys cahivinus

The common spiny mouse, Acomys cahirinus (body mass=47 g), is widely distributed in Israeli deserts where it inhabits natural crevices on rocky slopes. This omnivorous rodent consumes a varied diet, and in particular snails. We determined diet selection and energy and water balances of spiny mice when they were offered snails and seeds. The spiny mice maintained steady state body mass. Dry matter consumption of snails was 0.014 g* g⁻¹.-d⁻¹ and of seeds was 0.049g*.g⁻¹d⁻¹ for a total of 0.063 g*g⁻¹*d⁻¹. Total water intake was 0.101ml-g⁻¹.d⁻¹ and metabolizable energy intakewas 0.990 kJ. gxs^-1.d⁻¹ for a ratio (ml: kJ) of 0.102. This ratio was similar to that reported in a previously published study on free-living spiny mice. We concluded that snails and seeds allowed spiny mice to fulfil their energy and water requirements with minimal dry matter and fresh matter intakes. Furthermore, spiny mice selected a diet that provided them with a water (ml) to energy (kJ) ratio of approximately 0.1, although it appeared that they are able to survive on a much drier diet.     

Breeding and fertility of the Egyptian spiny mouse, Acomys cahirinus: effect of different environments.

2 years experience with Acomys in one laboratory confirmed the slow breeding rate found by other workers. On moving the animals to another laboratory there was a 2-5 fold increase in breeding rate. The most likely explanation of this change was the presence of copper in the drinking water at the 1st laboratory, due to the use of copper water pipes. The data relating to maintenance and breeding of acomys for 2 years at the 2nd laboratory were analyzed to provide a more representative picture of the species.     

Local variation in helminth burdens of Egyptian spiny mice (Acomys cahirinus dimidiatus) from ecologically similar sites: relationships with hormone concentrations and social behaviour

Populations of Egyptian spiny mice (Acomys cahirinus dimidiatus) in a fragmented montane wadi system in the Sinai showed significant differences in the abundance of gut helminths. Differences in parasite load between populations were positively associated with measures of androgen activity but showed no significant relationship with glucocorticoid activity. Social discrimination tests with adult males from different wadis showed that those from sites with greater helminth abundance were less likely to investigate odours from other males and were less aggressive when subsequently interacting with the odour donors. Subjects showed markedly more investigation towards the odours of males from distant wadis compared with those from their own or immediately neighbouring wadi, but were less aggressive when confronted with odour donors from distant wadis. Despite this, there was a positive relationship between the amount of investigation towards distant male odour and subsequent aggression towards the male. While aggressiveness was positively associated with measures of androgen and glucocorticoid activity, no significant relationship emerged with individual helminth infection. Thus aggressiveness appeared to relate to overall local population levels of infection rather than individual challenge.     

The reproductive tract of the male spiny mouse (Acomys cahirinus) and coagulation studies with other species

The testes of the spiny mice showed asymmetry, the left being significantly heavier than the right (P = 0.025). Histological studies indicated that spermatozoa were first present in the testes of animals 35--45 days of age but the maturation of the accessory glands, especially the lateral prostates and coagulating glands, occurred later. The highest fructose concentration in the adult was in the lateral prostates (126.97 +/- 22.23 mg fructose/100 g, n = 5) and coagulating glands (99.38 +/- 17.65 mg fructose/100 g gland weight, n = 5). Coagulation tests of mixtures of extracts of seminal vesicles and coagulating glands from spiny mice and rats indicated that the vesiculase of the spiny mouse was active on rat substrates and vice versa. Cross-reactions of extracts of house mouse (Mus musculus), hamster (Mesocricetus auratus), gerbil (Meriones unguiculatus), and guinea-pig (Cavia porcellus) seminal vesicles (substrate) and coagulating glands (vesiculase) with those of rats and spiny mice showed that although the substrates of rat and spiny mouse were readily coagulated by vesiculase from all the other species, rat and spiny mouse vesiculase were not equally active on substrates of the other species.